Author ORCID Identifier
Year of Publication
Doctor of Philosophy (PhD)
Dr. Kunlei Liu
Chemical looping combustion (CLC) is a promising technology that can mitigate the carbon emissions for power generation. The cost of oxygen carriers (OCs) impedes the scale up of CLC. Compared to synthetic iron-based OCs, red mud (RM), an abundant iron-based solid waste from industry, is a cost-effective choice due to its intrinsic inclusion of both inert and catalytic phases that are crucial for CLC. It was anticipated that the addition of copper oxide to RM using a mechanical mixing method that can be easily scaled up would enhance both reactivity and oxygen transport capacity (OTC), and the heat of reaction was expected to be balanced. However, the low strength of copper poses a challenge for the attrition resistance of this OC, thereby limiting the amount of CuO addition. To ensure thermoneutrality, 5 wt.% CuO was added to RM. This research aims to understand attrition mechanisms of copper-supplemented red mud oxygen carrier (RMCuO OC) for CLC.
Firstly, the thermodynamic and kinetic performance of CuO addition to RM were evaluated via thermo-gravity analysis (TGA) under dry and wet conditions (e.g., with the presence of water vapor). RMCuO OC was prepared by mechanical mixing and calcination. According to the TGA results, the OTC of RMCuO was greater than RM in dry and wet conditions due to the present CuO. Moreover, the OTC improvement of RMCuO was larger in wet condition compared to dry condition due to the limited reduction degree of iron oxide at the thermodynamic equilibrium according to the phase diagram, which was verified by the XRD patterns of attrition fines from fluidized bed reactor (FBR). Moreover, the differentiation of TGA (DTG) showed that the kinetic reaction rate of RMCuO was larger than RM. It is also confirmed by FBR experiment that the temperature shows decreased difference between reduction and oxidation per mole of oxygen in RMCuO compared to RM, indicating improved energy balance.
Secondly, the effect CuO addition on the durability of RMCuO OC was evaluated in TGA and FBR. RMCuO OC was stable over 100 cycles in the TGA reactor and 70 cycles in FBR; moreover, RMCuO has a lower attrition rate than RM OC in the 70 cycles. The reacted RMCuO has similar mechanical strength compared to RM OC, and no agglomeration was observed. Besides, cycled RMCuO showed an increase in elastic modulus and ratio of modulus to hardness, leading to lower attrition rates compared to cycled RM, demonstrating that the mechanical integrity was ensured. The particle attrition rate was determined by chemical and mechanical stresses at the steady stage. Based on scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) results, the iron and copper in the RMCuO OC particles migrated outward from the bulk to the surface and then formed an enriched dense layer, leading to the increased smoothness on the surface, which reduced the attrition rate of RMCuO OC in the steady stage. Moreover, it is found that the surface morphology of RMCuO OC was primarily affected by temperature, as it involved a competitive kinetic between the growth of needle-like structure and outward migration of iron and copper. At lower temperatures below 950 °C, the surface was porous and covered with needles, while at higher temperatures above 950 °C, the surface was smoother and denser. This suggests that higher temperatures in CLC may benefit the surface integrity for RMCuO OC.
Furthermore, the upgrade of iron ore was evaluated through the OC attrition. The attrition occurred in the FBR tests is due mainly to surface abrasion, resulting in the formation of fines with an ore-grade concentration of iron and trace amount of copper oxide with the outward migration and enrichment of iron and copper on the surface layer of OC. These purified fines as a valuable byproduct for commodity, making RMCuO a cost-effective oxygen carrier for CLC. Moreover, the addition of CuO increased the magnetic susceptibility of OC, increasing the ability to magnetically recycle the attrition fines from ash in solid-fuel CLC.
Lastly, the application of CLC was extended to the material recovery of spent Li-ion battery. By calculating the phase distribution via FactSage and test on TGA, it was found that the valuable Cobalt, Nickel, and Lithium can be effectively separated and recycled.
Digital Object Identifier (DOI)
This study was supported by China Scholarship Council (2019-2023) and the internal support of University of Kentucky (2019-2023)
Huang, Neng, "Attrition Study of Copper-Supplemented Iron-Based Oxygen Carrier for Chemical Looping Combustion" (2023). Theses and Dissertations--Mechanical Engineering. 210.
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